Summary The Sikorsky S-76A helicopter, serial number 760214, departed Vancouver Harbor helipad at about 1238 Pacific daylight time (PDT) with two pilots and eight passengers on board for a flight to the Vancouver International Airport. When the pilot decelerated for landing, he experienced a high-frequency vibration in the collective pitch lever. He continued the approach using the minimum power required and noted that the intensity of the vibrations was reduced. During the final phase of the approach, the pilot noticed low intensity vibrations in the tail rotor pedals. He carried out a no-hover landing and taxied to the hangar without further incident. There were no injuries or damage. Ce rapport est galement disponible en franais. Other Factual Information Company maintenance personnel determined that the vibrations were the result of a broken tail rotor pitch control rod assembly (Sikorsky part number 76103-05003-041, serial number A063-00899). The broken pitch control rod assembly was removed and forwarded to the TSB Engineering Branch for inspection and analysis. The tail rotor pitch control rod assembly consists of a link and two rod end assemblies. The rod end assemblies, each consisting of a rod end and a bearing, are threaded into the ends of the link and are retained in place by a nut and locking device. Following installation on the helicopter, the tail rotor pitch control rod assemblies are maintained as on condition units and are not required to be removed or overhauled in accordance with any specified time frame. Item 8 in the 50-hour inspection checklist, detailed in maintenance manual SA 4047-76-2-1, Dec.98, Chapter 5-20-00, states Tail rotor pitch control rods and pitch beam for damage and security. Rod end bearings for condition. There is also no requirement to track the part's service history. The broken component of the pitch control rod assembly was the rod end (Sikorsky part number 76103-05002-102), and it was found broken adjacent to the nut. The Sikorsky S-76A four-bladed tail rotor consists of two opposing blade pairs, joined at the hub, constituting an inner pair and an outer pair. The pitch control rod assemblies for each of the two pairs are identical, except that the assemblies connected to the inner blade pair are longer than those connected to the outer blade pair. This length differential is achieved by adjustment of the rod ends. The rod end assemblies are the subject of Sikorsky Alert Service Bulletin (ASB) 76-65-45, first issued 11 March 1994 and reissued 08 June 1994 as ASB 76-65-45A. The Canadian Aviation Regulations (CARs) do not require operators to comply with a manufacturer's bulletins. Neither the U.S. Federal Aviation Authority, who oversees the S-76 design, nor Transport Canada has issued an Airworthiness Directive in relation to this Service Bulletin. The purpose of Sikorsky ASB 76-65-45 and 76-65-45A is to perform a one-time inspection of the tail rotor control rod assemblies for cracks in the exposed threaded areas of the rod ends. A visual inspection is to be performed for cracks and corrosion pits using a 10X power magnifying glass. If no crack indication or corrosion pits are found, a fluorescent penetrant inspection is to be performed on the exposed threaded areas on both rod ends of the four control rod assemblies to determine if a crack is present. If a crack indication or corrosion pits are found, the rod end is to be replaced. Sikorsky ASB 76-65-45 and 76-65-45A inspections are specific to the rod ends (Sikorsky part number 76103-05002-102 and 76103-05002-101) and not to the helicopter. The ASB requires, upon accomplishment of the instructions, an appropriate logbook entry be made to show compliance with this ASB. Helijet Airways Inc. recorded compliance with Sikorsky ASB 76-65-45 on the incident helicopter on 14 May 1994 with an accumulated airframe time of 14 940 hours total time since new (TTSN). At the time of the pitch control rod assembly removal, the helicopter had accumulated 21 412 hours TTSN. The pitch control rod assembly failed after 6472 hours, and about four years and one month after the Sikorsky ASB 76-65-45 had been complied with. Helijet Airways Inc. did not have a record of the TTSN for the pitch control rod assembly, nor were they required to. With respect to detecting cracks in the tail rotor pitch control rod ends, the Sikorsky S-76 approved Maintenance Manual (Revision 31) does not specify an inspection, nor does it contain details as to how to perform such an inspection. The Maintenance Manual does, however, identify the need to inspect the pitch control rod assemblies for corrosion, but only on the exposed threads of the rod ends, and only if the protective paint /corrosion preventive compound has been degraded. The Maintenance Manual details the inspection procedures for the pitch control rod and damper bearings and identifies corrosion prevention procedures for the tail rotor pitch control rods including the rod end threaded area. The mode of failure was determined to be high cycle fatigue; the fracture propagated under normal service loads from fatigue-generated pre-cracks originating from the region of the thread root, close to the corners of the keyway. The crack initiated in the first full thread outboard of the bearing housing, an area that is exposed. Fatigue was found to be coincident with the stress concentration provided by the thread roots in the presence of corrosion pitting. Similar failures have been recorded by Sikorsky. The TSB Engineering Branch report states the tail rotor pitch control rod bearing radial play was found to be within Sikorsky's published limits; however, the metal-to-metal contact between the inner and outer bearing races appears to meet the Maintenance Manual requirement for replacement of the rod end. The TSB Engineering Branch report also states that the exposed threaded portions of the broken tail rotor pitch control rod did not have the required corrosion-preventative compounds applied. No traces of paint or other surface protection materials were detected.